You really have to think about CL transactions as the same as garage sales. Imagine if you had a garage sale, and someone came up to you asking about an item, you set a price and then they wanted to come back for it in (insert any length of time here) BUT - they didn't want to give you any money to hold it.
As the seller, would you agree to that? Of course not, because you are trying to sell the item for the best price you can, as quickly as you can. First money takes it. And what if that person never came back and there you are holding their (insert item here) and three other people approached you that day about the item, but you didn't sell it because you gave your word to that person who yet would not give you a deposit to hold the item?
On CL, I've found that the first person to show up with the money (and closer to full price, the better) gets the item. As a seller, I state this in my listings "first $50 takes it". As a buyer, I know that if I'm calling on a hot item that I *REALLY* want, I better high-tail it over ASAP with cash in hand. Furthermore, I *never* haggle ahead of seeing the item, nor do I ask if their price is firm. If I note a flaw after I arrive, THEN I inquire about a discount on the price. If you try to haggle before even seeing the item, your seller is not going to bend over backwards to complete THAT sale, when someone else can still offer him full price.
I'm sorry that happened to you, but I do see his case too. It would be hard for me to turn down full price from my *neighbor*, at that. Much easier to have a stranger mad at me than my neighbor friend, whom I see every day.